Scientific Utility of Emerging Indicators in Relative Energy Deficiency in Sport (REDs) Severity/Risk Assessment

Many emerging but non-validated indicators and biomarker thresholds have been used in the Relative Energy Deficiency in Sport (REDs) literature. Accordingly, we (1) compared the outcomes of the 2023 International Olympic Committee REDs Clinical Assessment Tool-version 2 (CAT2) (green, yellow, orange and red traffic light risk/severity assessment) with emerging REDs indicators, and (2) tested the utility of existing risk thresholds (clinical vs. subclinical biomarker cut-offs) for primary and secondary REDs indicators. Female (n = 143) and male (n = 70) athletes (performance tier 3-5) were assessed with the CAT2 and emerging REDs indicators featuring a self-report questionnaire, fasted blood analysis, resting blood pressure (BP) and heart rate (HR). Logistic regression was used to determine threshold cut-offs for blood biomarkers at which there was an 80% probability of REDs. Red-light athletes had significantly lower systolic BP (p < 0.001), HR (p = 0.009), white blood cell count (WBC; p = 0.018) and higher high-density lipoprotein cholesterol (p = 0.028) compared to green-light. Elevated cortisol: insulin ratio (p = 0.018), and reduced prolactin (p < 0.001) and luteinizing hormone (p < 0.05) concentrations were observed among higher-risk (orange + red) versus lower-risk (green + yellow) athletes. Males with total testosterone and triiodothyronine within the lowest quartile of reference range had an 80% probability of being classified as higher risk (orange + red) and history of BSI, respectively. For other outcomes at 80% probability, biomarkers were outside the clinical range. HR, systolic BP and WBC may be appropriate considerations for extreme (red-light) REDs diagnosis. More research with larger numbers of orange/red light athletes is needed to confirm findings and elucidate athlete-specific cut-offs for subclinically low biomarkers.